Disable Internet to Lan on Server side and only route Lan traffice via OpenVPN

[duke.brown]

Title says it all. I only want pfSense to route the Lan traffic through the VPN tunnel. I have another router that provides internet.

[viragomann]

Assign an interface to the OpenVPN instance in Interfaces > Assign.
Then edit all you LAN firewall rules which allow upstream traffic, open the advanced options, go down to Gateway and select the gateway of the corresponding OpenVPN instance.

Consider that rules with stated gateway only allow traffic passing that gateway. So if you also need access to other destinations like DNS on pfSense itself you have to add additional rules to permit that and put them to the top of the rule set.